When making anything with apples, I like to use a variety to ensure a balance in flavour and texture and flavour, sweetness and tartness. Ideally, I choose three or four varieties and leave some of the skin on each of them if it has not gone though from the apples being in storage. Taste them and decide. You want some of the apples to turn to applesauce and some to keep their shape for this crisp. Among the firmer apples are Granny Smith, Greening, Gravenstein and Winesap. Sweeter apples are Golden Delicious, Empire, Gala, and Fuji. The McIntosh on the East Coast and Pink Lady on the West Coast have a good sweet-tart balance and bake up softer.